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\psaxes[ticks=none,labels=none]{<->}(0,0)(-0.5,-0.5)(4.5,4)
\psplot[linecolor=blue]{0.5}{3.6}{2.7183^(x-2.5)+0.5}
\rput[b](3.6,3.5){$f$}
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\psxTick[ticksize=-3pt 0,labelsep=3pt](2.5){a}
\psline[linestyle=dashed,linecolor=gray](2.5,0)(2.5,1.5)(0,1.5)
\psyTick[ticksize=-3pt 0,labelsep=3pt](1.5){f(a)}
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\uncover<3->{
\psplot[linecolor=red]{0.5}{3.6}{1.5}
\rput[l](3.7,1.5){$p^0$}
}
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\psxTick[ticksize=-3pt 0,labelsep=3pt](3.5){x}
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\uncover<5->{
\psline{<->}(3.5,1.5)(3.5,3.2183)
\rput[l](3.6,2.3){$f(x)-p^0(x)$}
}
\end{pspicture*}